This invention relates to fluid separation membranes incorporating a molecular sieve material dispersed in a polymer.
The use of selectively gas permeable membranes to separate the components of gas mixtures is commercially very important art. Such membranes are traditionally composed of a homogeneous, usually polymeric, composition through which the components to be separated from the mixture are able to travel at different rates under a given set of driving force conditions, e.g. transmembrane pressure, and concentration gradients.
A relatively recent advance in this field utilizes mixed matrix composite (MMC) membranes. Such membranes are characterized by a heterogeneous, active gas separation layer comprising a dispersed phase of discrete particles in a continuous phase of a polymeric material. The dispersed phase particles are microporous materials that have discriminating adsorbent properties for certain size molecules. Chemical compounds of suitable size can selectively migrate through the pores of the dispersed phase particles. In a gas separation involving a mixed matrix membrane, the dispersed phase material is selected to provide separation characteristics that improve the permeability and/or selectivity performance relative to that of an exclusively continuous phase polymeric material membrane.
U.S. Pat. Nos. 4,740,219, 5,127,925, 4,925,562, 4,925,459, 5,085,676, 6,508,860, 6,626,980, and 6,663,805, which are not admitted to be prior art with respect to the present invention by their mention in this background, disclose information relevant to mixed matrix composite membranes. U.S. Pat. Nos. 4,705,540, 4,717,393, 4,880,442, and U.S. Patent Publication Nos. 20040107830 and 20040147796, which are not admitted to be prior art with respect to the present invention by their mention in this background, disclose polymers relevant to permeable gas separation membranes. However, these references suffer from one or more of the disadvantages discussed herein.
Permselective membranes for fluid separation are used commercially in applications such as the production of oxygen-enriched air, production of nitrogen-enriched-air for inerting and blanketing, separation of carbon dioxide from methane or nitrogen, and the separation of helium from various gas streams. It is highly desirable to use membranes, such as MMC membranes, that exhibit good permeabilities, and good permselectivities in these applications. It is particularly desirable to use asymmetric membranes in these applications. It is also desirable to produce MMC membranes that exhibit consistent permeation performance. However, some polymers do not provide improved MMC membrane performance when used to form asymmetric membranes. Furthermore, some polymers have shown to exhibit an interaction with components of the process streams, such as organic solvents, that can result in the loss of performance due to plasticizing the membrane or other problems.
It remains highly desirable to provide a mixed matrix gas separation membrane having molecular sieve material dispersed in a continuous polymer matrix that yield improved permeation performance, particularly when making asymmetric membranes. It is also desirable that MMC membranes of any form show a consistent permeation performance. Finally, it is desirable to maintain permeation performance after exposure to gas mixtures with aggressive process compositions, such as compositions containing organic solvents or contaminants.